PROJECT SUMMARY The field of taste has identified several regulatory molecules that direct development of the fungiform papilla: the sense organ residence of taste buds on the anterior tongue. However, the complexity of the papilla taste organ, composed of specific signaling compartments and encompassing both epithelial and connective tissues, has been ignored. Furthermore, specific differences in gene expression in fungiform papilla-forming versus papilla-free tongue regions have not been explored. This application focuses on the concept that only with knowledge about gene expression and protein localization in particular regions of the tongue and compartments of the fungiform papilla can a clear understanding emerge about how papilla development is regulated. Tongue regions and papilla compartments are physiological units that integrate signals to balance cell responses of proliferation or differentiation. Thus, cell signaling proceeds in the confines of particular compartments that then signal back and forth to define papilla induction, development and differentiation. The working hypothesis is that the important morphogen, Sonic hedgehog controls fungiform papilla development, in a concentration dependent manner, through: (a) signaling to regulate cell proliferation in specific compartments and tongue regions; and, (b) interactions with signaling other molecular families. Approaches to test the hypothesis include use of reporter and transgenic mice; tongue organ cultures; gene arrays; and gene knockdown with siRNAs via transfection and electroporation. Three specifc aims are to: Probe stage and compartment specific roles for the important morphogen, Sonic hedgehog (Shh), in cell proliferation versus differentiation. Define, and explore roles for, compartment specific genes in the developing tongue and tongue cultures, comparing lingual tissues in conditions that are papilla-replete, papilla-superabundant, papilla-suppressed, or papilla-free. Determine interactions among Shh, Wingless (Wnt) and Bone morphogenetic protein (Bmp) families. Studies will add crucial depth to understanding fungiform papilla formation; depth that is essential to knowing how papilla- and taste cell- specific compartments arise. In turn knowledge about signaling compartments in papilla differentiation is fundamental to pursuing questions about the origins of specific taste cell constitution, control of papilla and taste cell renewal, and papilla and taste cell plasticity during development. This knowledge is essential for acquiring basic information about how taste sensation emerges, to ultimately direct our diet and food choices.